Mobile wireless communication apparatuses becoming widespread in recent years are required to have high throughput, and a PLL (Phase Locked Loop) circuit operating in a high-frequency band as a frequency synthesizer in wireless communications is requested to be used.
The PLL circuit includes a frequency divider for frequency-dividing a high-frequency signal into a low-frequency signal. An ILFD (Injection Locked Frequency Divider) capable of operating at high speed with low power consumption in a high-frequency band of 10 GHz or more for example is used as a frequency divider. The injection locked frequency divider is hereafter simply referred to as “ILFD” as necessary.
In the ILFD, a frequency band (hereafter referred to as “locking range”) in which the ILFD operates as a frequency divider for frequency-dividing an injection signal (input signal) is narrow; hence, calibration in which the control voltage of the ILFD for changing the locking range according to the frequency of an injection signal is required so that the ILFD operates as a frequency divider in a high-frequency band (for example, a millimeter wave band) (for example, refer to Patent Document 1).